Piping Plover (Charadrius melodus) demography, behavior, and movement on the Outer Banks of North Carolina
The Piping Plover (Charadrius melodus) is an imperiled shorebird that inhabits sandy beaches along the North American Atlantic Coast. The species' decline has been attributed to habitat loss, disturbance, and predation throughout its range, although most conservation efforts have focused on increasing reproductive output during the breeding season. On the coast of North Carolina, Piping Plovers breed in areas with large amounts of recreational and tourism use. Beach recreation is known to reduce nest success, chick survival, and potentially fitness in other parts of the species' range. To reduce potential negative effects from human activities on breeding Piping Plovers, managers close areas to pedestrian and vehicle access using exclusion buffers delineated by symbolic fencing. However, the reproductive success and population size of Piping Plovers in parts of North Carolina has not appeared to increase as a result of these management strategies, despite the importance of the park and its protections to these birds on their southward migration in the fall.
To understand how disturbance and attempts to mitigate it affected plover demography, we examined Piping Plover population dynamics, brood movement, and migration in North Carolina from 2015–2017. We monitored 46 nests and 19 broods, and we used a logistic exposure nest survival model and Cormack-Jolly-Seber model to estimate reproductive success. We uniquely banded 77 adults and 49 chicks to understand annual survival and fidelity rates using a live encounter mark-recapture model. During the pre-fledge period, we observed movements of Piping Plover broods, and we gathered information on their environment that may affect their behavior. We recorded 191 brood locations, collected 132 focal chick behavior samples, and 113 potential disturbance environmental samples. We used multiple linear regression to evaluate several hypotheses regarding daily and hourly brood movement rates. We also conducted 22 migratory surveys after the breeding season in 2016 at an area in Cape Hatteras National Seashore thought to be used by large numbers of south-bound migrating Piping Plovers. We used integrated Jolly-Seber and binomial count models on resighting and count data to estimate stopover superpopulation and stopover duration of migrating birds based on their breeding region of origin.
Annual survival of adults from North Carolina (x ̅ = 0.69, SE = 0.07) was not different from another population on Fire Island, New York (x ̅ = 0.73, SE = 0.04), but the North Carolina population annually had low reproductive success, primarily due to low rates of chick survival. As a result, the North Carolina population was predicted to decline during the study period (λ<1 each year). Historically this population has not met the estimated rate of reproductive output needed for a stationary population (1.07 chicks per pair, SE = 0.69); therefore, it is likely the population is sustained by immigration from an unknown source. Daily (x ̅ = 71.5m/24hr) and hourly (x ̅ = 183.3m/hr) brood movements each had considerable variation (Daily: SD = 70.6, range = 0.0–327.2m; Hourly: SD = 262.3, range = 0.2–1450.9m). Chicks did not appear to move in response to the environmental factors we examined. The rate of brood movement suggests regular daylight monitoring is necessary to adequately protect unfledged broods from anthropogenic disturbance under current management methods. We found that 569 Piping Plovers (95% CI: 502–651), nearly 15% of the estimated Atlantic Coast population, stopped at a single area in Cape Hatteras National Seashore, North Carolina during fall migration. Birds stayed an average 4–7 weeks, depending on the breeding region from which they migrated, and they primarily used a relatively new protected area. These findings suggest that North Carolina is an important area for Piping Plover ecology during multiple stages of their annual cycle.